Chilled Ceilings / Beams Working Principles & Applicationsenergyinst.org.hk/Activity/ICE2014/3.4 Dr...
Transcript of Chilled Ceilings / Beams Working Principles & Applicationsenergyinst.org.hk/Activity/ICE2014/3.4 Dr...
Chilled Ceilings / Beams Working Principles & Applications
Francis W H Yik
ATAL Building Services Engineering Ltd.
16 October 2014
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5th International Conference on Energy – Sustainable Energy Polices and Technologies 15-17 October 2014
Contents
Chilled Ceilings / Beams
Working Principles & Application
Introduction
Operating principles
Key advantages and concerns
Application to buildings in Hong Kong – Trial calculations
Experience with pilot installations
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Introduction
Energy Consumption
58% Overall Reduction in
Chilled ceilings or chilled beams are widely used in buildings designed for an
energy use level below those of conventional
buildings by 50% or more
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Introduction
• Chilled ceiling / beam originated and are widely used in Europe
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Introduction
• Chilled ceiling / beam are penetrating the US market
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Introduction
• Chilled ceiling / beam projects in Beijing
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Introduction
• Chilled ceiling / beam projects in Guangzhou • PEARL RIVER TOWER
• 2.3 million sq ft • 71 storeys, 310m
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Introduction
• Chilled ceiling / beam projects in Hong Kong
# Project Project Nature System installed Area (m2)
Year of Completion Owner/ User
1 HAECO CLK Building - Office Renovation Chilled Ceiling 720 2011 HAECO
2 Chinese University, meeting room Renovation Chilled Beam 8 2012 Chinese University
3 Wong & Ouyang BS Ltd. Office, Renovation Chilled Beam 250 2013 W&O BS Ltd.
4 Hang Seng Tower, 10 Floors Renovation Chilled Beam 10,000 2013 Hang Seng Bank
5 Hang Seng Management College, Block D, 3/F – 8/F (6 Floors) New Construction Chilled Ceiling 5,000 2013 Hang Seng
Management College
6 HSBC Data Centre at STTL 433, Shek Mun, Shatin, 7/F – 10/F office New Construction Chilled Ceiling +
Chilled Beam 9,000 2013 HSBC
7 Hong Kong Science Park Phase 3, Conference Room New Construction Chilled Beam 80 in progress HK Science Park
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Introduction
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What are the key concerns that hinder wider adoption of chilled ceilings / beams in buildings in Hong Kong?
How can the perceived problems be resolved?
Operating principles
• Comfort air-conditioning
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Heat exchange of human body with the environment
Heat transfer by convection, C
Heat transfer by radiation, R
Operating principles
• Comfort air-conditioning
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Heat exchange of human body with the environment
Heat transfer by convection, C
Heat transfer by radiation, R
Conventional AC system
AHU
FA EA
SA
RA Ch. W S&R
Operating principles
• Comfort air-conditioning
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Heat exchange of human body with the environment
Heat transfer by convection, C
Heat transfer by radiation, R
Conventional AC system
AHU
FA EA
SA
RA Ch. W S&R
• Actively controlling the indoor air temperature, ta
• No active control over the temperatures of surfaces enclosing the space
Operating principles
• Comfort air-conditioning
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Heat exchange of human body with the environment
Heat transfer by convection, C
Heat transfer by radiation, R
Conventional AC system
AHU
FA EA
SA
RA Ch. W S&R
• Actively controlling the indoor air temperature, ta
• No active control over the temperatures of surfaces enclosing the space
tr = mean radiant temperature (a weighted mean value of temperatures of all surfaces to which the occupant is exposed)
Operating principles
• Comfort air-conditioning
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Heat exchange of human body with the environment
Heat transfer by convection, C
Heat transfer by radiation, R
Conventional AC system
AHU
FA EA
SA
RA Ch. W S&R
• Actively controlling the indoor air temperature, ta
• No active control over the temperatures of surfaces enclosing the space
• Operative temperature, to, represents the combined effect of ta and tr
tr = mean radiant temperature (a weighted mean value of temperatures of all surfaces to which the occupant is exposed)
cr
acrro hh
ththt++
=
Operating principles
• Comfort air-conditioning
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Heat exchange of human body with the environment
Heat transfer by convection, C
Heat transfer by radiation, R
Conventional AC system
AHU
FA EA
SA
RA Ch. W S&R
• Actively controlling the indoor air temperature, ta
• No active control over the temperatures of surfaces enclosing the space
• Operative temperature, to, represents the combined effect of ta and tr
tr = mean radiant temperature (a weighted mean value of temperatures of all surfaces to which the occupant is exposed)
cr
acrro hh
ththt++
=
Operating principles
• Comfort air-conditioning
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Heat exchange of human body with the environment
Heat transfer by convection, C
Heat transfer by radiation, R
Conventional AC system
AHU
FA EA
SA
RA Ch. W S&R
• Actively controlling the indoor air temperature, ta
• No active control over the temperatures of surfaces enclosing the space
• Operative temperature, to, represents the combined effect of ta and tr
tr = mean radiant temperature (a weighted mean value of temperatures of all surfaces to which the occupant is exposed)
cr
acrro hh
ththt++
=
Lowering mean radiant temperature (tr) allows
indoor air temperature (ta) to be raised without affecting operative
temperature (to) and thus thermal comfort sensation
of occupants
Operating principles
• Comfort air-conditioning
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Heat exchange of human body with the environment
Heat transfer by convection, C
Heat transfer by radiation, R
PAU
OA EA
PA
RA Ch. W S&R
Ch. W S&R
Chilled ceiling panels
DOAS or PA system
DOAS = Dedicated Outdoor Air System PA = Primary Air 17
Operating principles
• Comfort air-conditioning
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Heat exchange of human body with the environment
Heat transfer by convection, C
Heat transfer by radiation, R
PAU
OA EA
PA
RA Ch. W S&R
Ch. W S&R
Chilled ceiling panels
DOAS or PA system
DOAS = Dedicated Outdoor Air System PA = Primary Air 18
Sensible heat only
Sensible and latent heat
Sensible heat only
Operating principles
• Chilled ceiling
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Operating principles
• Chilled ceiling
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Where the cooling requirement exceeds the capacity limit of chilled ceiling panels (~80W/m2), chilled beams may be used instead
Operating principles
• Chilled beam
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Operating principles
• Chilled beam
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The cooling capacity of passive chilled beams can be up to 350 - 475W/m2 (Based on their exposed face area – clearance spaces needed between chilled beams)
Operating principles
• Chilled beam
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Active chilled beam
Operating principles
• Chilled beam
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The cooling capacity of active chilled beams can be up to 700 - 1250W/m2 (Based on their exposed face area – even greater clearance spaces needed between chilled beams)
Active chilled beam
Operating principles
• Key characteristics of a chilled ceiling or chilled beam system:
There must be two systems operating in parallel:
• Chilled ceiling panels or
chilled beams • Which extract (only)
sensible heat from the spaces
• A primary air (PA) system or dedicated outdoor air system (DOAS)
• Which supply ventilation air as well as remove ALL moisture gains (latent cooling loads) and a fraction of the sensible heat gains of the spaces
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Key advantages and concerns
• Key advantages
Radiant cooling by using chilled ceiling
• Enhances thermal comfort
and
• Allows use of slightly higher indoor dry-bulb temperature set point
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ASHRAE Handbook, HVAC Systems and Equipment, 2008, Chapter 6 Panel Heating and Cooling Principal advantages of panel systems are the following: • Because not only indoor air
temperature but also mean radiant temperature can be controlled, total human thermal comfort may be better satisfied.
• Comfort levels can be better than those of other space-conditioning systems because thermal loads are satisfied directly and air motion in the space corresponds to required ventilation only.
Key advantages and concerns
• Key advantages
• Separation of dehumidification (solely by PA system) from sensible cooling (by both PA system and chilled ceiling / beams) allows:
• Air flow rate (VPA < VSA), and thus fan power and noise, to be reduced (although fan power saving also achievable in VAV systems)
• Use of higher temperature chilled water for the chilled ceilings / beams, which helps save chiller energy use (low temp. Ch.W. still needed for PA system unless desiccant dehumidification is used)
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Key advantages and concerns
• Key advantages
• Reduced ceiling space required for installation
• Reduced maintenance cost
• When controlled properly, will not promote the formation of condensate which can lead to bacterial and mould growth
• Do not require drain pans which require cleaning
• Do not contain fans or filters to maintain and require only simple periodic service including vacuuming of the dry coil
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Key advantages and concerns
Must ensure:
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r
s
wr ws
tr ts
• The PA supply flow rate (VPA) is sufficient, and the difference in moisture content between the indoor air and the PA supply (wr−ws) is large enough for the PA to offset the total moisture gain (Mr) of the room
)( srPAar wwVM −= ρ
Key advantages and concerns
Must ensure:
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r
s
wr ws
tr ts
• The surface temperatures of the chilled ceilings / beams must be above the dew point temperature of the indoor air (tdpr)
)( srPAar wwVM −= ρ
tdpr
Key advantages and concerns
Must ensure:
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• The total sensible cooling capacity of the chilled ceilings / beams (QSCC/B) is sufficient to offset the remainder of the room sensible load (with the sensible cooling effect of the PA discounted)
QSR = Design room sensible cooling load QSPA = Sensible cooling capacity of PA Where Required sensible cooling capacity of chilled ceilings / beams QSCC/B >= QSR – QSPA
)( sraPAaSPA ttCpVQ −= ρ
Key advantages and concerns
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• Key concerns
• Stagnant air flow and cold air dumping onto occupants
• Condensation risk
• Limited cooling capacity of
chilled ceiling / beam modules Impact on whether CC/B can be used
Key advantages and concerns
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• Key concerns
• Stagnant air flow and cold air dumping onto occupants
• Condensation risk
• Limited cooling capacity of
chilled ceiling / beam modules
• Can be overcome by careful building and system design and operation
• Maintain at least 1m clear headroom between passive chilled beam and occupied zone (1.7m from finished floor level)
• Use active chilled beam
• Adequate selection and layout of chilled beams and/or diffusers for PA
• Raise PA supply flow rate if absolutely needed
Key advantages and concerns
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• Key concerns
• Stagnant air flow and cold air dumping onto occupants
• Condensation risk
• Limited cooling capacity of
chilled ceiling / beam modules
• Can be overcome by careful building and system design and operation
• Minimize moisture gains of spaces
• Ensure PA system has sufficient dehumidification capacity; if needed, use heat pipes or desiccant dehumidification
• Use an appropriate Ch.W supply temperature setting
• Monitor and control ceiling / beam surface temperature
Key advantages and concerns
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• Key concerns
• Stagnant air flow and cold air dumping onto occupants
• Condensation risk
• Limited cooling capacity of
chilled ceiling / beam modules
• Can be overcome by careful building and system design and operation
• Minimize envelope heat gains
• Use energy efficient lighting
• Use energy efficient appliances
• Use active chilled beams
Application to buildings in Hong Kong
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Design conditions Unit Value
Design OA temperature, To oC 33.3 Design OA RH, RHo % 66 Design OA moisture content, wo kg/kg 0.02146 Design OA enthalpy, ho kJ/kg 88.47
Design RA temperature, Tr oC 25 Design RA RH, RHr % 55 Design RA dew point, Tdpr oC 15.4 Design RA moisture content, wr kg/kg 0.01093 Design RA enthalpy, hr kJ/kg 52.982
Room floor area (Interior Zone) m2 493.24 Room height m 3.2 Room volume m3 1578.368
Lighting and app. power density W/m2 35 Lighting and appliances heat gain, Qsi kW 17.2634
Design conditions Unit Value
Occupancy rate m2/p 9 No. of Occupants No. 54.8 Sensible heat gain per person W/p 75 Rad. Sen. heat gain from occupant % 60 Latent heat gain per person W/p 55 Moisture gain per person g/s-p 0.0219912 Sensible load from occupants, Qsp kW 4.1103333 Latent heat gain from occupants, Qlp kW 3.0142444 Moisture gain from occupants, Mp kg/s 0.0012052
FA requirement l/s-p 10 FA flow rate, Vfa m3/s 0.5480444
Infiltration ACH ACH 0.1 Infiltration flow rate, Vinf m3/s 0.0438436 Sensible load from infiltration, Qsinf kW 0.4439598 Latent load from infiltration, Qlinf kW 1.3855719 Moisture gain from infiltration, Minf kg/s 0.000554
• Trial calculations – reference conditions (office building in HK)
Application to buildings in Hong Kong
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• Trial calculations – cooling load intensity
Design cooling load predictions for Model Office Building by BEEP
Floor Space DSL DLL DTL Area DSL DLL DTL kW kW kW m2 W/m2 W/m2 W/m2
Typical North 11.33 1.46 12.79 144.44 78.42 10.13 88.54 Typical West 14.39 1.20 15.58 144.44 99.59 8.30 107.90 Typical East 13.07 1.86 14.94 144.44 90.51 12.91 103.42 Typical South 12.33 1.12 13.45 144.44 85.34 7.77 93.11 Typical Interior 25.75 6.04 31.79 493.24 52.20 12.25 64.45
Typical SimTot 73.67 11.05 84.73 1071.00 68.79 10.32 79.11
Application to buildings in Hong Kong
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• Trial calculations – cooling load intensity
Design cooling load predictions for Model Office Building by BEEP
Floor Space DSL DLL DTL Area DSL DLL DTL kW kW kW m2 W/m2 W/m2 W/m2
Typical North 11.33 1.46 12.79 144.44 78.42 10.13 88.54 Typical West 14.39 1.20 15.58 144.44 99.59 8.30 107.90 Typical East 13.07 1.86 14.94 144.44 90.51 12.91 103.42 Typical South 12.33 1.12 13.45 144.44 85.34 7.77 93.11 Typical Interior 25.75 6.04 31.79 493.24 52.20 12.25 64.45
Typical SimTot 73.67 11.05 84.73 1071.00 68.79 10.32 79.11
Shared between chilled ceilings / beams and PA system By PA system
Application to buildings in Hong Kong
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• Trial calculations – PA flow rate
0
0.5
1
1.5
2
2.5
3
9 10 11 12 13 14
PA S
uppl
y Fl
ow R
ate
m3/
s
PA Supply Dew Point Temperature oC
FA Flow Rate
25oC / 55% RH (tdpr 15.40oC)
24oC / 55% RH (tdpr 14.41oC)
25oC / 50% RH (tdpr 13.87oC)
24oC / 50% RH (tdpr 12.95oC)
Indoor design temperature, relative
humidity and dew point temperature
Application to buildings in Hong Kong
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• Trial calculations – PA flow rate
0
0.5
1
1.5
2
2.5
3
9 10 11 12 13 14
PA S
uppl
y Fl
ow R
ate
m3/
s
PA Supply Dew Point Temperature oC
FA Flow Rate
25oC / 55% RH (tdpr 15.40oC)
24oC / 55% RH (tdpr 14.41oC)
25oC / 50% RH (tdpr 13.87oC)
24oC / 50% RH (tdpr 12.95oC)
Indoor design temperature, relative
humidity and dew point temperature
The higher the tdpr, the smaller the Vpa
The lower the tdps, the smaller the Vpa
The required PA supply flow rate (Vpa) is highly sensitive to the choices of the indoor air state (tdpr) and the PA supply air state (tdps)
Application to buildings in Hong Kong
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• Trial calculations – PA flow rate
0
0.5
1
1.5
2
2.5
3
9 10 11 12 13 14
PA S
uppl
y Fl
ow R
ate
m3/
s
PA Supply Dew Point Temperature oC
FA Flow Rate
25oC / 55% RH (tdpr 15.40oC)
24oC / 55% RH (tdpr 14.41oC)
25oC / 50% RH (tdpr 13.87oC)
24oC / 50% RH (tdpr 12.95oC)
Indoor design temperature, relative
humidity and dew point temperature
Selected condition: Sensible cooling provided by PA = 18.13W/m2
Application to buildings in Hong Kong
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• Trial calculations – Required chilled ceiling / beam cap.
Floor Space DSL PA S Cap CC/B Cap W/m2 W/m2 W/m2
Typical North 78.42 18.13 60.29 Typical West 99.59 18.13 81.46 Typical East 90.51 18.13 72.38 Typical South 85.34 18.13 67.21 Typical Interior 52.20 18.13 34.07
• Chilled beams need to be used for the perimeter zones but chilled ceilings may be used for the interior zone
Application to buildings in Hong Kong
• Key design considerations
• Minimize sensible cooling load through
• Reducing external heat gains by improving thermal performance of building envelope
• Reducing internal heat gains by using energy efficient lighting and appliances
• Minimize latent cooling load through reducing ingress of humid air into air-
conditioned space by
• Improving air-tightness of building envelope
• Positive pressurization of air-conditioned space
• Use of anteroom (lobby with double-door) if needed
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Application to buildings in Hong Kong
• Key design considerations
• Adequate selection of design indoor air state (an increase in RH by 5% can make a big difference)
• Adequate selection of design PA supply air state (the lower the moisture content in it the smaller the required PA supply flow rate), subject to the constraints of
• Temperature of chilled water supply to PAU (may use desiccant dehumidification)
• Minimum FA supply flow rate for air-conditioned spaces
• Adequate selection of temperature of chilled water supply to chilled ceilings / beams (at or slightly above dew point temperature of indoor air)
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Experience with pilot installations
• Hui & Leung (2012)
• Study on chilled ceiling application in Hong Kong
• Simulation results: ~20% energy saving achievable
• Field study – offices of an aircraft engineering company:
• Chilled ceiling in use since mid-2011
• 84% of the occupants satisfied with thermal sensation, though 40% felt temperature sometimes too hot
• 51% felt air movement too low
• Findings similar for another field study (construction site office)
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Experience with pilot installations
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Experience with pilot installations
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Experience with pilot installations
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Experience with pilot installations
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End of Presentation
Thank you
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